There are over three-quarters of the world's population who have been using mobile communication devices such as mobile phones or tablet computers. When using a mobile phone or a tablet computer, a user has to grasp these devices for a long time, in which the posture leads to the suppression of nerves in an arm, and thus the arm becomes numb. When the numbness in arms gets serious, the user often has to go to a doctor. Similarly, when reading books, people need to hold the books with both of their hands. After reading books for a long time, the readers' hands become numb and sore.
In the past, some hands-free devices are introduced to solve the above mentioned problems. The conventional products for mobile phone include earphones and headset-microphone for making and receiving phone calls. With earphones or headset microphones, the users do not need to hold their mobile phone with hands; instead, the users only need to keep the mobile phone fixed in their pockets or in the handbags, or dispose their mobile phone on the mobile phone supporters. On the other hands, the prior products for tablet computers include foldable cover cases which can be folded into necessary shapes to support the tablet computers. Furthermore, some manufacturers develop a kind of hands-free device for books, in which the device includes an adjustable metal tube with a book-clamping tool. The metal tube can be adjusted according to different reading postures such as lying flat position, sitting position, or standing position. Therefore, the readers can read the books without holding them. However, currently there are limited types of hands-free holders. People who want to use hands-free reading devices for mobile phone, tablet computers and books need to buy these three types of hands-free reading devices respectively. Having to separately buy these three types of hands-free reading devices is disadvantageous for the users, since it is costly to buy three kinds of devices. Besides, it is also inconvenient to use three kinds of devices separately.